Sewing With Nancy, I think, had the lady on that started all of this. She has a website but I don't remember what it was. Maybe this is it. It has directions anyway.
http://www.littledressesforafrica.org/blog/?page_id=477
I'd set it up like an assembly line(s) and change positions every half hour or so. That way everyone would get to do everything. With an assembly line you'll be able to put out a LOT more dresses than if everyone is trying to do everything at once. Have some of the women bring their machines, others their irons and ironing boards, some could bring fabric, others thread and still others embellishments such as rick rack, braid, buttons, etc., some should bring elastic.